It is frequently desirable to measure a force, such as a compression, tension, torque or weight force, and control or limit the amount of force. For example, during drilling of oil and gas wells, sections of pipe, approximately 30 feet in length, are connected to form a longer length by thread engagement of the male end of the pipe into the female end of the next joint of pipe. It is necessary to apply a precalculated, but limited, amount of torque during the makeup to assure sufficient thread engagement and also effect a fluid tight seal. Power tongs, such as the LAMB Model 16,000, may be used for this operation and consist of jaws to firmly grip the pipe and hydraulic power to rotate the jaws. A back-up arm, to prevent rotation of the tong assembly, is tied to a corner leg of the derrick by a length of cable. The applied torque can then be monitored by inserting a tension measuring transducer in line with the back-up cable and the arm length times the tension is the applied torque.
In the past, a hydraulic system composed of a tension member, hydraulic connecting hose and a dial readout was the most popular device used. The operator observed the torque gauge and when sufficient torque was indicated, he manually shut off hydraulic tong power. Other prior art devices which indicate when a "bad joint" or a "good joint" has been made up are illustrated in U.S. Pat. Nos. 3,368,396; 3,606,664; and 3,745,820.
Another example of the use of a force measuring and controlling apparatus is for measuring and limiting the weight of a substance such as a batch of concrete.